Atomistic theoretical study of electronic and polarization properties of single and vertically stacked elliptical InAs quantum dots

Usman, Muhammad

doi:10.1103/physrevb.86.155444

Cited by 31 publications

(32 citation statements)

References 49 publications

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“…The region where the biaxial strain is relaxed has now slightly moved towards the left edges of the QDLs, with the right edges being under stronger negative biaxial strain, especially for the higher QDLs. Noticeably, the large negative biaxial strain on the right edge of the QD9 will lead to the creation of hole pocket in the QD9 layer much similar to the ones earlier observed for the single 25,28 and stacked 6 QDs. As will be sown next, this will lead to the confinement of hole wave functions in the QD9 layer along the [110]-direction, thereby considerably impacting the polarization properties.…”

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confidence: 73%

Electronic and optical properties of [110]-tilted InAs/GaAs quantum dot stacks

Usman¹

2014

Phys. Rev. B

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Multi-million atom simulations are performed to study stacking-angle (θ) dependent strain profiles, electronic structure, and polarization-resolved optical modes from [110]-tilted quantum dot stacks (QDSs). Our calculations reveal highly asymmetrical biaxial strain distributions for the tilted QDSs that strongly influence the confinements of hole wave functions and thereby control the polarization response. The calculated values of degree of polarizations, in good agreement with the available experimental data, predict a unique property of the tilted QDSs that the isotropic polarization response can be realized from both [110] and [-110] cleaved-edges − a feature inaccessible from the conventional [001]-QDSs. Detailed investigations of polar plots further establish that tilting the QDSs provides an additional knob to fine tune their polarization properties. for the same number of QDLs in both stacks. Furthermore, a large rotation of PL polar plot peak was measured from the [-110] cleaved-edge surface leading to a discrepancy with the angle of tilt of the QDS. This appealed for a detailed understanding of the stacking-angle dependent electronic and optical properties to appropriately explain the experimental measurements. This work presents a first theoretical study of the tilted InAs QDSs by performing atomistic simulations of strain, electronic structure, and polarization-dependent inter-band optical transition strengths. The unique characteristics of the tilted QDSs are reported by highlighting highly asymmetrical biaxial strain distributions that regulate the electronic structure and polarization properties. It is predicted that by tilting the QDS, isotropic polarization response could be simultaneously realized from both [110] and [-110] cleaved- edge surfaces − a feature not accessible from the conventional [001]-aligned stacks [5][6][7] . The comparison of polar plots further revealed a high degree of control over the polarization properties attainable by tilting the QDSs, making it a useful tool for engineering the optical properties from the QD nano-structures.

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confidence: 73%

Electronic and optical properties of [110]-tilted InAs/GaAs quantum dot stacks

Usman¹

2014

Phys. Rev. B

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“…The atomistic simulations are performed using NanoElectronic MOdeling tool NEMO-3D [27,28], which has previously shown to quantitatively match the experimental data sets for a variety of nanostructures and nanomaterials, such as shallow donors in Si [8,22], III-V alloys [29,30] and quantum dots [31][32][33], SiGe quantum wells [34], etc. The sp 3 d 5 s * tight-binding parameters for Si material are obtained from Boykin et al [35], that have been optimised to accurately reproduce the Si bulk band structure.…”

Section: Methodsmentioning

confidence: 99%

Donor hyperfine Stark shift and the role of central-cell corrections in tight-binding theory

Usman

Rahman

Salfi

et al. 2015

J. Phys.: Condens. Matter

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Atomistic tight-binding (TB) simulations are performed to calculate the Stark shift of the hyperfine coupling for a single Arsenic (As) donor in Silicon (Si). The role of the central-cell correction is studied by implementing both the static and the non-static dielectric screenings of the donor potential, and by including the effect of the lattice strain close to the donor site. The dielectric screening of the donor potential tunes the value of the quadratic Stark shift parameter (η2) from -1.3 × 10 −3 µm 2 /V 2 for the static dielectric screening to -1.72 × 10 −3 µm 2 /V 2 for the non-static dielectric screening. The effect of lattice strain, implemented by a 3.2% change in the As-Si nearest-neighbour bond length, further shifts the value of η2 to -1.87 × 10 −3 µm 2 /V 2 , resulting in an excellent agreement of theory with the experimentally measured value of -1.9 ± 0.2 × 10 −3 µm 2 /V 2 . Based on our direct comparison of the calculations with the experiment, we conclude that the previously ignored non-static dielectric screening of the donor potential and the lattice strain significantly influence the donor wave function charge density and thereby leads to a better agreement with the available experimental data sets.

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“…The physical insights presented in this section will serve as a basis to understand the effects of electric fields in the later sections of this paper. The lowest three electron states (e1, e2, e3) and the highest four hole states (h1, h2, leading to the lower p-state being aligned along the [-110] direction [5,31]. Therefore all of the hole states in the QDM are aligned along this direction.…”

Section: − Theoretical Frameworkmentioning

confidence: 99%

“…Self-assembled quantum dot molecules (QDMs) made up of III-V materials are one of the most popular types of nanostructures used in a variety of devices for optoelectronic [1][2][3][4][5][6][7], photovoltaic [8][9][10][11][12], and quantum information technologies [13,14]. The QDMs typically grow in the form of vertical stacks due to the presence of strain, which stems from the lattice mismatch of the substrate and the QD material.…”

Section: − Introductionmentioning

confidence: 99%

Understanding the electric field control of the electronic and optical properties of strongly-coupled multi-layered quantum dot molecules

Usman

2015

Nanoscale

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Strongly-coupled quantum dot molecules (QDMs) are widely deployed in the design of a variety of optoelectronic, photovoltaic, and quantum information devices. An efficient and optimized performance of these devices demands engineering of the electronic and optical properties of the underlying QDMs. The application of electric fields offers a knob to realise such control over the QDM characteristics for a desired device operation. We perform multi-million-atom atomistic tight-binding calculations to study the influence of electric fields on the electron and hole wave function confinements and symmetries, the ground-state transition energies, the band-gap wavelengths, and the optical transition modes. The electrical fields both parallel ( E p ) and anti-parallel ( E a ) to the growth direction are investigated to provide a comprehensive guide on the understanding of the electric field effects. The strain-induced asymmetry of the hybridized electron states is found to be weak and can be balanced by applying a small E a electric field, of the order of 1 KV/cm. The strong interdot couplings completely break down at large electric fields, leading to single QD states confined at the opposite edges of the QDM. This mimics a transformation from a type-I band structure to a type-II band structure for the QDMs, which is a critical requirement for the design of intermediate-band solar cells (IBSC). The analysis of the field-dependent ground-state transition energies reveal that the QDM can be operated both as a high dipole moment device by applying large electric fields and as a high polarizibility device under the application of small electric field magnitudes. The quantum confined Stark effect (QCSE) red shifts the band-gap wavelength to 1.3 µm at the 15 KV/cm electric field; however the reduced electron-hole wave function overlaps lead to a decrease in the interband optical transition strengths by roughly three orders of magnitude. The study of the polarisation-resolved optical modes indicate the benefit of applying small electric fields, which lead to an isotropic polarisation response, a desirable property for the semiconductor optical amplifiers (SOAs).1 arXiv:1508.05981v1 [cond-mat.mes-hall]

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Atomistic theoretical study of electronic and polarization properties of single and vertically stacked elliptical InAs quantum dots

Cited by 31 publications

References 49 publications

Electronic and optical properties of [110]-tilted InAs/GaAs quantum dot stacks

Electronic and optical properties of [110]-tilted InAs/GaAs quantum dot stacks

Donor hyperfine Stark shift and the role of central-cell corrections in tight-binding theory

Understanding the electric field control of the electronic and optical properties of strongly-coupled multi-layered quantum dot molecules

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